Glaucoma is a leading cause of blindness. An elevated intraocular pressure (lOP) is a major risk factor. We have been studying the 24-hour pattern of lOP under strictly controlled laboratory conditions. Data have been collected from healthy young and elderly volunteers, from untreated glaucoma patients/suspects, and from glaucoma patients treated with timolol or latanoprost. In order to know whether or not surgical treatment sufficiently reduces lOP in glaucoma patients at night, we will study the 24-hour pattern of lOP in glaucoma patients receiving laser trabeculoplasty (Aim 1). An elevated lOP alters the ocular perfusion pressure and consequently may affect ocular blood flow. How the 24-hour variation of lOP affects ocular blood flow is unknown. Ocular blood flow may very well vary independently from lOP over the 24 hours. Therefore, we will study the 24-hour pattern of ocular blood flow in healthy individuals (Aim 2). Blood flow in the retrobulbar blood vessels will be characterized using the color Doppler imaging technique in the laboratory. Young and elderly volunteers will be selected based upon their home recordings of ambulatory blood pressure, sleep conditions, and lOP. Since an abnormal ocular blood flow may be another risk factor for glaucoma, we will study the 24-hour pattern of ocular blood flow in glaucoma patients (Aim 3). Similar home recordings will be performed to select representative glaucoma patients with excessive dipping of nocturnal blood pressure and with sleep apnea. Laboratory data will be collected from untreated glaucoma patients/suspects and from glaucoma patients receiving medical treatment with timolol or latanoprost and those surgically treated with laser trabeculoplasty. The long-term goal of the proposed studies is to define the endogenous mechanisms in the regulation of human lOP and ocular blood flow. Experimental results should provide fundamental information about how ocular blood flow is regulated during the day and at night in healthy individuals. New knowledge of ocular blood flow and lOP in patients would have implications for the better diagnosis and treatment of glaucoma.